Methods for forming isolated fin structures on bulk semiconductor material

ABSTRACT

Methods are provided for fabricating a semiconductor device. A method comprises forming a layer of a first semiconductor material overlying the bulk substrate and forming a layer of a second semiconductor material overlying the layer of the first semiconductor material. The method further comprises creating a fin pattern mask on the layer of the second semiconductor material and anisotropically etching the layer of the second semiconductor material and the layer of the first semiconductor material using the fin pattern mask as an etch mask. The anisotropic etching results in a fin formed from the second semiconductor material and an exposed region of first semiconductor material underlying the fin. The method further comprises forming an isolation layer in the exposed region of first semiconductor material underlying the fin.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. application Ser. No. 12/575,344, filed Oct.7, 2009, and issued on Jan. 24, 2012 as U.S. Pat. No. 8,101,486.

TECHNICAL FIELD

Embodiments of the subject matter generally relate to semiconductordevice structures and related fabrication methods, and moreparticularly, embodiments of the subject matter relate to methods forforming semiconductor device structures having conductive fins which areelectrically isolated from a bulk semiconductor substrate.

BACKGROUND

Transistors, such as metal oxide semiconductor field-effect transistors(MOSFETs), are the core building block of the vast majority ofsemiconductor devices. Some semiconductor devices, such as highperformance processor devices, can include millions of transistors. Forsuch devices, decreasing transistors size, and thus increasingtransistor density, has traditionally been a high priority in thesemiconductor manufacturing industry.

A FinFET is a type of transistor that can be fabricated using very smallscale processes. FIG. 1 is a simplified perspective view of a FinFET100, which is formed on a semiconductor wafer substrate 102. A FinFET isnamed for its use of one or more conductive fins 104. As shown in FIG.1, each fin 104 extends between a source region 106 and a drain region108 of FinFET 100. FinFET 100 includes a gate structure 110 that isformed across fins 104. The surface area of the fins 104 in contact withgate structure 110 determines the effective channel of FinFET 100.

FinFET devices have historically been formed using silicon-on-insulator(SOI) substrates. Using an SOI substrate, the conductive fins are formedfrom the silicon material, while the insulator layer provides isolationbetween adjacent FinFET devices. Bulk silicon substrates are lessexpensive than SOI substrates, and FinFET devices can also be fabricatedusing bulk silicon if appropriate isolation methodologies are utilized.

BRIEF SUMMARY

A method is provided for fabricating a semiconductor device on a bulksubstrate. The method comprises forming a layer of a first semiconductormaterial overlying the bulk substrate and forming a layer of a secondsemiconductor material overlying the layer of the first semiconductormaterial. The method further comprises creating a fin pattern mask onthe layer of the second semiconductor material and anisotropicallyetching the layer of the second semiconductor material and the layer ofthe first semiconductor material using the fin pattern mask as an etchmask. The anisotropic etching results in a fin formed from the secondsemiconductor material and an exposed region of first semiconductormaterial underlying the fin. The method further comprises forming anisolation layer in the exposed region of first semiconductor materialunderlying the fin.

Another method is provided for manufacturing a finned semiconductordevice structure. The method comprises providing a substrate comprisingbulk semiconductor material, a layer of a first semiconductor materialon the bulk semiconductor material, and a layer of a secondsemiconductor material on the layer of the first semiconductor material.The method further comprises selectively removing portions of the layerof second semiconductor material and the layer of first semiconductormaterial, which results in a fin formed from the second semiconductormaterial overlying an exposed region of first semiconductor material.The method further comprises forming an isolation layer in the exposedregion of first semiconductor material.

In another embodiment, a method for fabricating a semiconductor deviceis provided. The method comprises providing a bulk substrate formed froma bulk semiconductor material, forming a layer of a first semiconductormaterial overlying the bulk semiconductor material, and forming a layerof a second semiconductor material overlying the layer of the firstsemiconductor material. The second semiconductor material has anoxidation rate that is less than the oxidation rate of the firstsemiconductor material. The method further comprises creating a finpattern mask on the layer of the second semiconductor material andanisotropically etching the layer of the second semiconductor materialusing the fin pattern mask as an etch mask, which results in a finformed from the second semiconductor material. Anisotropically etchingthe layer of the second semiconductor material also removes portions ofthe first semiconductor material, resulting in an exposed region offirst semiconductor material underlying the fin. The method furthercomprises oxidizing the exposed region of first semiconductor materialunderlying the fin, such that the fin is electrically isolated from thebulk semiconductor material.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the subject matter may be derived byreferring to the detailed description and claims when considered inconjunction with the following figures, wherein like reference numbersrefer to similar elements throughout the figures.

FIG. 1 is a simplified perspective view of a conventional FinFET havinga plurality of fins; and

FIGS. 2-8 illustrate, in cross section, a semiconductor device structureand exemplary methods for fabricating the semiconductor device structurein exemplary embodiments.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. As used herein, the word“exemplary” means “serving as an example, instance, or illustration.”Any implementation described herein as exemplary is not necessarily tobe construed as preferred or advantageous over other implementations.Furthermore, there is no intention to be bound by any expressed orimplied theory presented in the preceding technical field, background,brief summary or the following detailed description.

Techniques and technologies described herein may be utilized tofabricate MOS transistor devices, including NMOS transistor devices,PMOS transistor devices, and CMOS transistor devices. Although the term“MOS device” properly refers to a device having a metal gate electrodeand an oxide gate insulator, that term will be used throughout to referto any semiconductor device that includes a conductive gate electrode(whether metal or other conductive material) that is positioned over agate insulator (whether oxide or other insulator) which, in turn, ispositioned over a semiconductor substrate. Various steps in thefabrication of semiconductor devices are well known and so, in theinterest of brevity, many conventional steps will only be mentionedbriefly herein or will be omitted entirely without providing the wellknown process details.

A variety of FinFET devices and related fabrication processes are known.In accordance with the traditional manufacturing techniques, conductivefins in a FinFET device are formed using photolithography, etching, andother conventional process steps. FinFET performance is dependent on theheight, thickness, and pitch of fins, and these dimensions should beuniform and closely controlled during manufacturing. In this regard,fabricating FinFETs using modern semiconductor manufacturing processes(e.g., 22 nm and smaller technologies) can be challenging due to theimportance of controlling the dimensions of the fins. The fabricationtechniques described herein can be utilized to precisely control the findimensions—in particular, the fin height—of fin structures formed from abulk semiconductor substrate.

The techniques and technologies described herein can be utilized to formfin structures for finned semiconductor devices, using a bulksemiconductor substrate rather than an SOI substrate. In this regard,FIGS. 2-6 are cross sectional views that illustrate an embodiment of afinned semiconductor device structure and a related fabrication method.This fabrication process represents one implementation of a method thatis suitable for use with finned semiconductor devices, such as FinFETsor other multi-gate transistor devices. In practice, however, thefabrication process could be used to form semiconductor fins that areultimately used for other semiconductor devices.

Referring now to FIG. 2, in an exemplary embodiment, the fabricationprocess begins by providing an appropriate bulk substrate 200, forming afirst layer of semiconductor material 204 overlying the bulk substrate200, and forming an upper layer of semiconductor material 206 overlyingthe intermediate layer of the semiconductor material 204. In thisregard, the first layer of semiconductor material 204 is alternativelyreferred to herein as the intermediate layer or the intermediatesemiconductor material, and the second layer of semiconductor material206 is alternatively referred to herein as the upper layer of uppersemiconductor material. FIG. 2 depicts the semiconductor devicestructure 208 after forming the layers of semiconductor material 204,206 overlying the bulk substrate 200. It should be appreciated that thefabrication of a finned semiconductor device need not always begin witha bulk substrate, but rather, an embodiment of the fabrication processmay instead begin with the semiconductor device structure 208 depictedin FIG. 2. Thus, a suitably pre-fabricated wafer could be obtained froma vendor, where the pre-fabricated wafer would have bulk semiconductormaterial having an intermediate layer of semiconductor material formedon the bulk semiconductor material, and an upper layer of semiconductormaterial formed on the intermediate layer of semiconductor material.Accordingly, fabrication of the fin structures described herein maybegin by providing such a pre-fabricated wafer or substrate.

As described in greater detail below, in an exemplary embodiment, theoxidation rate of the intermediate semiconductor material 204 is greaterthan the oxidation rate of the upper semiconductor material 206, suchthat an exposed region of the intermediate semiconductor material 204underlying the upper semiconductor material 206 may be fully consumedduring subsequent oxidation while leaving the upper semiconductormaterial 206 substantially intact, thereby isolating the uppersemiconductor material 206 from the bulk semiconductor material 202. Inthis regard, the oxidation rate of the intermediate semiconductormaterial 204 is preferably at least three times greater than theoxidation rate of the second semiconductor material 206.

In an exemplary embodiment, the bulk substrate 200 is formed from orotherwise comprises a semiconductor material 202 (alternatively referredto herein as the bulk semiconductor material). The bulk semiconductormaterial 202 is preferably a silicon material as typically used in thesemiconductor industry, e.g., relatively pure silicon as well as siliconadmixed with other elements such as germanium, carbon, and the like.Alternatively, bulk semiconductor material 202 can be germanium, galliumarsenide, or the like. The bulk semiconductor material 202 need not bedoped, although it may be very lightly doped as either N-type or P-type,without impacting the manufacturing process described here. For example,bulk silicon substrates are often provided as lightly doped P-typesubstrates, and a lightly doped P-type semiconductor material 202 couldbe used for the embodiment described here. Of course, the bulksemiconductor material 202 can be subsequently doped in an appropriatemanner to form active regions in a manner that is well understood bythose familiar with semiconductor manufacturing techniques.

In accordance with one or more embodiments, the intermediate layer ofsemiconductor material 204 is formed by epitaxially growing a layer of adifferent type of semiconductor material on the bulk semiconductormaterial 202. In an exemplary embodiment, the bulk semiconductormaterial 202 comprises silicon, wherein the intermediate layer ofsemiconductor material 204 is formed by epitaxially growing a siliconmaterial on the bulk semiconductor material 202. Preferably, theintermediate semiconductor material 204 is realized as silicon germaniumwhich is grown on an exposed surface of the bulk semiconductor material202 in accordance with known process techniques. It should be noted thatother materials having the same general properties and characteristicscould be used in lieu of silicon germanium. That said, silicon germaniumis commonly used for other purposes in semiconductor manufacturingprocesses, is accepted for use in the industry, and is well documented.Accordingly, preferred embodiments employ silicon germanium for theintermediate semiconductor material 204.

As described in greater detail below, in an exemplary embodiment, as theratio of the oxidation rate of the intermediate semiconductor material204 to the oxidation rate of the upper semiconductor material 206increases, the thickness of the intermediate semiconductor material 204decreases. For example, when realized as silicon germanium, depending onthe embodiment, the thickness of the semiconductor material 204 mayrange from about 10 nanometers (nm) to about 100 nm. The oxidation rateof the silicon germanium layer 204 is directly related to its germaniumconcentration, as will be appreciated in the art. Preferably, theintermediate semiconductor material 204 has a germanium concentration ofgreater than about ten percent germanium. Accordingly, when theintermediate semiconductor material 204 is realized as silicon germaniumhaving a germanium concentration of about ten percent germanium, thethickness of the intermediate semiconductor material 204 may be greaterthan the thickness of the intermediate semiconductor material 204 whenthe intermediate semiconductor material 204 is realized with greatergermanium concentration. In an exemplary embodiment, the intermediatesemiconductor material 204 comprises silicon germanium having agermanium concentration of about thirty percent germanium and athickness of about 30 nm.

In accordance with one or more embodiments, the upper layer ofsemiconductor material 206 is formed by epitaxially growing it on theexposed surface of the intermediate layer of semiconductor material 204.In an exemplary embodiment, the bulk semiconductor material 202comprises silicon and the intermediate semiconductor material 204comprises silicon germanium, wherein the upper layer of semiconductormaterial 206 is formed by epitaxially growing silicon on the silicongermanium that forms the intermediate layer of semiconductor material204. In this regard, the upper semiconductor material 206 and the bulksemiconductor material 202 comprise the same material, e.g., silicon,however, the use of the same semiconductor material is not alwaysrequired, and alternate embodiments could utilize different materialsfor bulk semiconductor material 202 and the upper semiconductor material206. Epitaxial silicon can be grown on silicon germanium in accordancewith known process techniques, as described briefly above. In practice,second semiconductor material 206 has a thickness in the range of about20 to 50 nm, although thicknesses outside of this typical range could beutilized. Notably, semiconductor material 206 will ultimately be used toform conductive fin structures. Therefore, semiconductor material 206preferably comprises device quality silicon that can be epitaxiallygrown with little or no defects or contamination. It should be notedthat other materials having these properties and characteristics couldbe used for the upper semiconductor material 206 (in lieu of silicon).That said, preferred embodiments will utilize silicon for the uppersemiconductor material 206.

In an exemplary embodiment, the fabrication process continues by formingtwo layers of insulating material 214, 216 overlying the upper layer ofsemiconductor material 206 and removing portions of the layers ofinsulating material 214, 216 to create and define a fin pattern mask210. In certain embodiments, first layer of insulating material 214 isformed from an oxide material. This oxide material may be a thermallygrown silicon dioxide formed by heating semiconductor device structure212 in an oxidizing ambient, or it may be a deposited material such assilicon oxide. Alternatively, first layer of insulating material 214could be silicon nitride, a high-k dielectric material such as hafniumcompound (e.g., hafnium silicate, hafnium oxide or hafnium siliconoxynitride), or the like. The insulating material 214 can be depositedby chemical vapor deposition (CVD), low pressure chemical vapordeposition (LPCVD), or plasma enhanced chemical vapor deposition(PECVD). In practice, first layer of insulating material 214 istypically about 5 nm to 30 nm in thickness. In preferred embodiments,second layer of insulating material 216 is formed by depositing siliconnitride on first layer of insulating material 214, to a thickness withinthe range of about 5 nm to 30 nm. In practice, silicon nitride can bedeposited onto first layer of insulating material 214 using, e.g.,LPCVD. The nitride material is preferable because it accommodates theselective etching of underlying semiconductor material 204, 206 whensubsequently used as an etch mask, and because it is a good oxygenbarrier. Alternatively, silicon oxynitride or amorphous orpolycrystalline silicon could be used for second layer of insulatingmaterial 216. Although the illustrated embodiment includes a lower oxidelayer and an upper nitride layer for creating the fin pattern mask 210,an alternate embodiment of the fin pattern mask 210 could have a lowernitride layer and an upper oxide layer. Furthermore, more than twolayers of insulating material could be employed. Moreover, in alternateembodiments (not shown), the fin pattern mask 210 includes only anoverlying layer of nitride material without an underlying layer of oxidematerial.

Still referring to FIG. 3, the fin pattern mask 210 can be formed usingprocess steps such as, without limitation: material deposition orformation; photolithography; spacer imaging; etching; and cleaning. Forinstance, a soft mask (formed from photoresist material) or a hard mask(formed using spacers) can be formed overlying semiconductor devicestructure to serve as an etch mask. Thereafter, the unprotected portionsof first layer of insulating material 214 and second layer of insulatingmaterial 216 can be anisotropically etched using an appropriate etchantchemistry, resulting in semiconductor device structure 212 shown in FIG.3. Thus, the fin pattern mask 210 is created from the insulatingmaterials 214, 216 overlying the upper layer of semiconductor material206 and represents a hard mask that includes masking features defined bythe remaining portions of the insulating materials 214, 216. Notably,fin pattern mask 210 depicted in FIG. 3 includes two featurescorresponding to two respective fins that are subsequently formed fromthe upper semiconductor material 206.

Referring now to FIG. 4, in an exemplary embodiment, the fabricationprocess continues by selectively removing portions of the uppersemiconductor material 206 and the intermediate semiconductor material204, resulting in a semiconductor device structure 226 having one ormore fins 218 formed from the upper semiconductor material 206, witheach fin 218 overlying an exposed region 222 (or neck region) of theintermediate semiconductor material 204. In an exemplary embodiment, thefabrication process selectively removes portions of the upper layer ofsemiconductor material 206 by anisotropically etching exposed portionsof the upper semiconductor material 206 using the fin pattern mask 210as an etch mask, which protects portions of the upper semiconductormaterial 206 underlying the fin pattern mask 210. In an exemplaryembodiment, the fabrication process employs an anisotropic etchant thatalso removes portions of the intermediate semiconductor material 204while using the fin pattern mask 210 as an etch mask, thereby exposingregions 223 of the intermediate semiconductor material 204 surroundingthe fins 218 (alternatively referred to herein as the surroundingregions). The selective etching also results in the creation or exposureof insulating caps 220 that reside on fins 218. The embodiment shown inFIG. 4 has composite insulating caps 220, each being formed from theremaining sections of the first and second layers of insulating material214, 216.

As shown in FIG. 4, by anisotropically etching the intermediatesemiconductor material 204 using the fin pattern mask 210 as an etchmask, the fabrication process exposes regions 222 of the intermediatesemiconductor material 204 underlying the fins 218. In an exemplaryembodiment, the intermediate layer of semiconductor material 204 isanisotropically etched to a depth relative to the base 224 of the fins218 (or bottom surface the upper layer of semiconductor material 206)such that the height of the exposed regions 222 relative to thesurrounding regions 223 of intermediate semiconductor material 204 isless than or equal to the width of the fins 218. In this regard, theheight of the exposed regions 222 is less than or equal to the width ofthe exposed regions 222. For example, depending on the embodiment, thewidth of the fins 218 may range from about 10 nm to about 20 nm, whereinthe intermediate semiconductor material 204 is etched to a depth ofabout 10 nm to 15 nm relative to the base 224 of the fins 218.Maintaining an aspect ratio for the exposed regions 222 where the widthis greater than or equal to the height of the exposed regions 222provides stability and/or support at the base of the fins 218 duringsubsequent process steps.

Referring now to FIG. 5, in an exemplary embodiment, the fabricationprocess continues by isolating (or insulating) the fins 218 from thebulk semiconductor material 202 by forming an isolation layer 228 thatcomprises an insulating material formed from the intermediatesemiconductor material 206. In an exemplary embodiment, the isolationlayer 228 is formed by performing a field oxidation process whichoxidizes the exposed surfaces of semiconductor material 204, 206. Duringthe field oxidation step, semiconductor device structure 226 of FIG. 4is exposed to an oxidizing ambient in an elevated temperature thatpromotes selective growth of oxide material at the exposed surfaces ofthe semiconductor material 204, 206 resulting in the semiconductordevice structure 234 of FIG. 5. Preferably, the exposed regions 222 ofthe intermediate semiconductor material 204 underlying the fins 218 arefully consumed during this field oxidation process, forming connectingregions 230 underlying fins 218. In this regard, in an embodiment wherethe intermediate semiconductor material 204 comprises silicon germanium,the connecting regions 230 underlying the fins 218 comprise an oxidematerial having a germanium concentration corresponding to the germaniumconcentration of the intermediate semiconductor material 204 prior tooxidation. In other words, the germanium concentration of theintermediate semiconductor material 204 prior to oxidation influencesthe germanium concentration of the oxide material of the connectingregions 230. In some practical embodiments, the germanium concentrationof the oxide material of the connecting regions 230 may be approximatelyequal to the germanium concentration of the intermediate semiconductormaterial 204 prior to oxidation. Although FIG. 5 depicts the entireintermediate layer of semiconductor material 206 as being fullyconsumed, in alternative embodiments, some portions of the intermediatelayer of semiconductor material 204 in the surrounding regions 223 mayremain intact after oxidation. By oxidizing the exposed regions 222 ofthe intermediate semiconductor material 204 underlying the fins 218 toform connecting regions 230, the fins 218 are electrically isolated fromeach other. Additionally, the fins 218 are electrically isolated fromthe bulk substrate material 202 which, in turn, reduces leakage current(e.g., through the fins 218 to the bulk substrate material 202) andreduces the impact of neighboring devices on the same bulk substrate200.

In practice, during the oxidation process, oxide material may also growon the exposed semiconductor material 206 of the sidewalls 232 and/orbase 224 of the fins 218. However, because the oxidation rate of theintermediate semiconductor material 204 is sufficiently greater than theoxidation rate of the upper semiconductor material 206, the exposedregions 222 underlying the fins 218 may be completely consumed withminimal oxide material formed on the sidewalls 232 and/or base 224 ofthe fins 218, which, in turn, preserves most (if not all) of theoriginal height and width of the fins 218. For example, in an exemplaryembodiment where the intermediate semiconductor material 204 comprisessilicon germanium having a germanium concentration of about thirtypercent germanium and the upper semiconductor material 206 comprisessilicon, the thickness of the isolation layer 228 formed on thesidewalls of the fins 218 ranges from about 3 nm to 5 nm while thethickness of the isolation layer 228 formed from the regions 222, 223 ofthe intermediate semiconductor material 204 is about 20 nm to 30 nm.

Although other fabrication steps or sub-processes may be performed afterforming the isolation layer 228, in accordance with one embodiment, thefabrication process continues by removing portions of the isolationlayer 228 on the sidewalls 232 of the fins 218 and forming a gatestructure 236 overlying the fins 218, resulting in the semiconductordevice structure 238 shown in FIG. 6. In an exemplary embodiment, theisolation layer 228 is removed from the sidewalls 232 of the fins 218 byisotropically etching the isolation layer 228 using an isotropic etchantthat selectively etches the isolation layer 228 without attacking theupper semiconductor material 206. For example, when the isolation layer228 comprises an oxide material, a hydrogen fluoride based etchant maybe utilized to isotropically etch the isolation layer 228. The isotropicetchant also removes portions of the isolation layer 228 from theregions 223 surrounding the fins 218, however, in some embodiments, thethickness of the isolation layer 228 in the surrounding regions 223 willremain adequate to prevent undesired parasitic capacitance between thegate structure 236 and the bulk semiconductor material 202.Additionally, it should be appreciated that although FIG. 6 depicts theinsulating material 214, 216 as remaining intact, in some embodiments,the isotropic etchant may also partially etch exposed portions of theinsulating material 214, 216 depending on the particular type ofinsulating material and etchant utilized. The gate structure 236 can becreated using a conventional gate stack module or any combination ofwell-known process steps. It should be appreciated that FIG. 6 is across sectional view of semiconductor device structure 238. Accordingly,gate structure 236 will actually be overlying only a section of each fin218, and gate structure 236 will follow the overall contour of fins 218,contacting respective sections of sidewalls 232 and insulating materials214, 216. In this regard, gate structure 236 “wraps” over fins 218 inthe manner generally depicted in FIG. 1. Thereafter, any number of knownprocess steps, modules, and techniques can be performed to complete thefabrication of one or more semiconductor devices that incorporate fins218. For example, the manufacturing process can be carried out tocomplete the fabrication of at least one transistor device that includesfins 218 and gate structure 236. These final process steps, and otherback end process steps, will not be described here.

Referring now to FIG. 7 and FIG. 8, in some embodiments, it may bedesirable that a semiconductor device subsequently formed fromsemiconductor device structure 234 has a thicker layer of insulatingmaterial in the regions 223 surrounding the fins 218, for example, toreduce unwanted parasitic capacitance between a gate structuresubsequently formed overlying the fins 218 and the bulk semiconductormaterial 202. In this regard, in accordance with one or moreembodiments, after forming the isolation layer 228 as described above inthe context of FIG. 5, the fabrication process continues by forming alayer of dielectric material 240 (alternatively referred to herein asthe dielectric layer) overlying the isolation layer 228 and the fins218. As shown in FIG. 7, the thickness of the dielectric layer 240 ispreferably chosen such that the dielectric material 240 fills thesurrounding regions 223 and any gaps between the fins 218 to a minimumheight that meets or exceeds the height of the fins 218. In an exemplaryembodiment, the layer of dielectric material 240 is formed byconformally depositing a dielectric material, such as silicon oxide,overlying the isolation layer 228 and the fins 218 by chemical vapordeposition (CVD), low pressure chemical vapor deposition (LPCVD), orplasma enhanced chemical vapor deposition (PECVD), resulting in thesemiconductor device structure 242 shown in FIG. 7. In this regard, inan exemplary embodiment, the isolation layer 228 and the dielectriclayer 240 each comprise an oxide material, however, it will beappreciated in the art that the deposited dielectric layer 240 may beless dense than the isolation layer 228. Additionally, the germaniumconcentration of the isolation layer 228 is greater than that of thedielectric layer 240, which will typically be negligible (although somegermanium may diffuse to the dielectric layer 240 at the interface withthe isolation layer 228 during subsequent high temperature processsteps).

Referring now to FIG. 8, in an exemplary embodiment, the fabricationprocess continues by removing portions of the dielectric layer 240 andthe isolation layer 228 by isotropically etching the dielectric material240 and the isolation layer 228 using an isotropic etchant thatselectively etches the dielectric material 240 and the isolation layer228 without attacking the semiconductor material 206 comprising the fins218, in a similar manner as described above. In this regard, theisotropic etchant removes portions of the isolation layer 228 from thesidewalls 232 of the fins 218. In an exemplary embodiment, thedielectric layer 240 and/or isolation layer 228 are etched to thicknessthat provides sufficient isolation in the surrounding regions 223between a subsequently formed gate structure and the bulk semiconductormaterial 202. In accordance with one embodiment, the upper surfaces 244of the remaining dielectric layer 240 and/or isolation layer 228 in theregions 223 surrounding the fins 218 are substantially uniform andsubstantially aligned with the base 224 of the fins 218, resulting inthe semiconductor device structure 246 shown in FIG. 8.

Although other fabrication steps or sub-processes may be performed afterremoving portions of the dielectric layer 240 and the isolation layer228, in an exemplary embodiment, the fabrication process continues byforming a gate structure overlying the fins 218 and the surroundingdielectric layer 240 and/or isolation layer 228 in a similar manner asdescribed above in the context of FIG. 6. Thereafter, any number ofknown process steps, modules, and techniques can be performed tocomplete the fabrication of one or more semiconductor devices thatincorporate fins 218.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or embodiments described herein are not intended tolimit the scope, applicability, or configuration of the claimed subjectmatter in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the described embodiment or embodiments. It should beunderstood that various changes can be made in the function andarrangement of elements without departing from the scope defined by theclaims, which includes known equivalents and foreseeable equivalents atthe time of filing this patent application.

1. A method of fabricating a semiconductor device on a bulk substrate,the method comprising: forming a layer of a first semiconductor materialoverlying the bulk substrate; forming a layer of a second semiconductormaterial overlying the layer of the first semiconductor material;creating a fin pattern mask on the layer of the second semiconductormaterial; anisotropically etching the layer of the second semiconductormaterial and the layer of the first semiconductor material using the finpattern mask as an etch mask, resulting in a fin formed from the secondsemiconductor material and an exposed region of first semiconductormaterial underlying the fin; and forming an isolation layer in theexposed region of first semiconductor material underlying the fin;wherein anisotropically etching the layer of the first semiconductormaterial comprises anisotropically etching the layer of the firstsemiconductor material to a depth relative to a base of the fin that isless than or equal to a width of the fin.
 2. The method of claim 1,wherein forming the isolation layer comprises growing an oxide materialfrom the exposed region of first semiconductor material.
 3. The methodof claim 1, wherein forming the isolation layer comprises oxidizing theexposed region of first semiconductor material to form an oxide materialunderlying the fin.
 4. The method of claim 3, wherein a germaniumconcentration of the oxide material corresponds to a germaniumconcentration of the first semiconductor material.
 5. The method ofclaim 1, wherein forming the layer of the first semiconductor materialcomprises epitaxially growing the layer of the first semiconductormaterial on the bulk substrate.
 6. The method of claim 5, the bulksubstrate comprising silicon, wherein epitaxially growing the layer ofthe first semiconductor material on the bulk substrate comprisesepitaxially growing a layer of silicon germanium on the bulk substrate.7. The method of claim 6, wherein the layer of silicon germanium has agermanium concentration greater than ten percent germanium.
 8. Themethod of claim 6, wherein forming the layer of the second semiconductormaterial comprises forming a layer of silicon overlying the layer ofsilicon germanium.
 9. The method of claim 1, wherein the firstsemiconductor material has a first oxidation rate and the secondsemiconductor material has a second oxidation rate, the first oxidationrate being greater than the second oxidation rate.
 10. The method ofclaim 1, further comprising: removing any portions of the isolationlayer formed on sidewalls of the fin; and forming a gate structureoverlying the fin.
 11. A method of manufacturing a finned semiconductordevice structure, the method comprising: providing a substratecomprising bulk semiconductor material, a layer of a first semiconductormaterial on the bulk semiconductor material, and a layer of a secondsemiconductor material on the layer of the first semiconductor material;selectively removing portions of the layer of second semiconductormaterial and the layer of first semiconductor material, resulting in afin formed from the second semiconductor material overlying an exposedregion of first semiconductor material; and forming an isolation layerin the exposed region of first semiconductor material; whereinselectively removing portions of the layer of first semiconductormaterial comprises anisotropically etching regions of the layer of thefirst semiconductor material surrounding the fin to a depth relative abase of the fin less than or equal to a width of the fin.
 12. The methodof claim 11, wherein forming the isolation layer comprises oxidizing theexposed region of first semiconductor material to isolate the fin fromthe bulk semiconductor material.
 13. The method of claim 12, wherein thefirst semiconductor material comprises silicon germanium having agermanium concentration greater than about ten percent, such thatoxidizing the exposed region of first semiconductor material results ina region of the isolation layer underlying the fin having a germaniumconcentration greater than about ten percent.
 14. The method of claim11, further comprising: forming a layer of an oxide material overlyingthe isolation layer and the fin; and removing portions of the layer ofthe oxide material such that an upper surface of the layer of the oxidematerial is substantially aligned with a base of the fin.
 15. A methodof fabricating a semiconductor device on a bulk substrate, the methodcomprising: forming a layer of a first semiconductor material overlyingthe bulk substrate; forming a layer of a second semiconductor materialoverlying the layer of the first semiconductor material; creating a finpattern mask on the layer of the second semiconductor material;anisotropically etching the layer of the second semiconductor materialand the layer of the first semiconductor material using the fin patternmask as an etch mask, resulting in a fin formed from the secondsemiconductor material and an exposed region of first semiconductormaterial underlying the fin; forming an isolation layer in the exposedregion of first semiconductor material underlying the fin; forming alayer of dielectric material overlying the isolation layer and the fin;and removing portions of the layer of dielectric material such that anupper surface of the layer of dielectric material is substantiallyaligned with a bottom of the fin, wherein removing portions of the layerof dielectric material comprises isotropically etching the layer ofdielectric material, wherein isotropically etching the layer ofdielectric material also etches any portions of the isolation layerformed on sidewalls of the fin.